Studies of Zeolite Acidity

该项目包括一系列关于沸石和相关材料中酸性问题的研究。对H-ZSM-5中的中间体进行了光谱学研究--核磁共振是主要工具--以表征其化学计量比和反应性已分别确定的物种；目标是确定中间体的结构，它们与沸石晶格相互作用的性质，以及它们进行进一步转化的势垒高度。通过制备和研究一系列表征良好的H-Y沸石的酸性，考察了各种脱铝程序的效果以及骨架和非骨架铝浓度的作用；所用的酸性替代物包括程序升温脱附和热重分析胺、烷烃裂解和碱金属中毒。制备了一系列金属取代的ZSM-5和AlPO-5分子系列，并对它们进行了测试，以确定这些材料的相对酸强度，并确定了保持金属离子在骨架中的必要条件。沸石作为催化剂和分离介质已广泛应用于石油和化工等行业。尽管如此，影响他们表现的因素却鲜为人知。这项工作为沸石和相关骨架材料的应用提供了一种更合理的设计方法，对合成沸石进行了更好的质量控制，并可能使已知或新的骨架材料在化学加工、环境控制等领域得到新的应用。

This project consists of a set of studies addressing the issue of acidity in zeolites and related materials. Intermediates in H-ZSM-5 are studied spectroscopically - nuclear magnetic resonance being the prime tool - to characterize species whose stoichiometry and reactivity have been established separately; the objectives are the determination of the structure of the intermediates, the nature of their interactions with the zeolite lattice, and the barrier heights for them to undergo further transformations. The effect of various dealumination procedures and the roles of framework and nonframework aluminum concentrations are examined by preparation of and investigation of the acidity of a series of well-characterized H-Y zeolites; acidity surrogates used include temperature- programmed desorption and thermal gravimetric analysis of amines, alkane cracking, and alkali-metal poisoning. A series of metal-substituted ZSM-5 and ALPO-5 molecular series are prepared and examined to determine the relative acid strengths of these materials and to determine the necessary conditions for maintaining the metal ions in the framework. Zeolites are already widely used in the petroleum and chemicals industries both as catalysts and separations media. Despite this, factors influencing their performance are poorly understood. This work promises an approach to more rational design for applications of zeolites and related framework materials, better quality control over synthetic zeolites, and possible new applications of known or new framework materials in chemical processing, environmental control, and other areas.